In recent years, there has been spread a virtualization technology that enables to logically divide one computer into a plurality of virtually independent virtual computers for operating the virtual computers. The virtual computer control technology has been mainly utilized in general-purpose large-scale computers. However, in recent years, the virtual computer control technology has started to be used in data centers using inexpensive computers on the basis of a PC (Personal Computer) architecture for the purpose of reducing the running cost such as reducing the number of physical computers, reducing the power consumption, and simplifying the management.
There are roughly proposed two schemes as the device control in the virtual computer system utilizing the virtualization technology.
The first scheme is a scheme according to which a virtual computer exclusively uses a device. Hereinafter, the first scheme is called as a dedicated scheme. In the dedicated scheme, a virtual computer exclusively uses a device. Therefore, in controlling a device, a processor is not required to execute a processing, taking into account sharing the device by a plurality of virtual computers, and generally, degradation of the performance resulting from virtualization is small. On the other hand, in the dedicated scheme, power consumption is large, as compared with a second scheme to be described below, because the electric power consumption rate increases as the number of physical devices increases.
The second scheme is a scheme according to which a plurality of virtual computers share a device in operation. Hereinafter, the second scheme is called as a shared scheme. In the shared scheme, a plurality of virtual computers share a device in operation. Therefore, in controlling a device, a processor is required to execute a processing, taking into account sharing the device by a plurality of virtual computers, and generally, degradation of the performance resulting from virtualization is large. On the other hand, power consumption is small as compared with the first scheme, because the number of physical devices in operation decreases.
As described above, the two schemes have trade-off relations with each other in the aspect of performance and power consumption. Accordingly, there is a demand for a device control technology which meets the requirements on performance and power consumption.
In the following, three patent literatures 1 through 3 are described as existing device control related technologies, and the technologies disclosed in patent literatures 1 through 3 are briefly described.
Patent literature 1 discloses a method for sharing a device while avoiding degradation of the performance by switching the device control scheme from a dedicated scheme to a shared scheme or from the shared scheme to the dedicated scheme, depending on a change in usage of a virtual device.
Patent literature 2 discloses a power consumption reducing method, in which power saving control of physical resources in an inactive state and to be shared by a plurality of virtual computers is enabled by managing usage of the physical resources of the virtual computers, using a management operating system for managing physical resources assigned to virtual computers.
Patent literature 3 discloses an information processing device for controlling hardware resources corresponding to respective operating systems (OSs), wherein input/output control is executed for a device by a direct I/O method when an OS issues a state control request requesting turning on the power to the device, and input/output control is executed for the device by an emulation method when an OS issues a state control request requesting turning off the power to the device.
However, in the methods disclosed in patent literatures 1, 3, it is impossible to reduce power consumption of a device, because there is no power saving control means for the device. Further, in the method disclosed in patent literature 2, although there is a means for saving the power of a device in an inactive state, there is no means for switching the device control scheme. Accordingly, in the case where a device is shared and controlled by a plurality of virtual computers, the performance may be degraded.